In factories such as chemical plants, high- and medium-pressure steam is produced with a package boiler or a waste-heat boiler for various purposes. Because this high- and medium-pressure steam is accompanied by excess steam according to the fluctuation in the demand thereof, effective utilization is required, as shown in FIG. 12. In the figure, excess steam is introduced into a high- and medium-pressure steam header 101, a steam turbine 102 is rotated with steam supplied from this high- and medium-pressure steam header 101, and a driven machine 103, such as a pump or a compressor, is driven by this torque. Steam emitted from the steam turbine 102 is introduced to a low-pressure steam header 104 in the form of low-pressure steam at about 0.3 MPa (gauge pressure). After the pressure of the low-pressure steam in the low-pressure steam header 104 is reduced to a predetermined pressure by a pressure release valve 105, the low-pressure steam is condensed by a condenser 106. The condensate water produced by the condenser 106 is supplied to the boiler again by a condensate water pump 107.
In the related art, although energy is recovered by obtaining power for a driven machine with excess steam in this manner, the energy of used low-pressure steam is wasted by the pressure release valve 105. Particularly in small- and medium-scale plants, such as pulp and paper mills and food plants, quite a lot of low-pressure steam is produced to no avail due to fluctuation in the operating load.
Patent Document 1 discloses a technique for efficiently utilizing excess steam in a case where such excess steam is produced due to an abrupt reduction in plant steam.